Flashlamp units employing solid state switching devices to fire a plurality of flashlamps individually and in sequence are well-known. In U.S. Pat. No. 3,458,270 there is disclosed such a switching arrangement having switch devices of silver oxide adhesively bonded to the substrate of an electrical circuit with an organic polymer binder. The particular flashlamps employed are further depicted to be of the low voltage type which upon battery ignition convert the switch devices in the electrical circuit to a "low ohmic" condition. The organic binder in the switch material composition is said to produce a chain of reduction and oxidation reactions with the silver oxide which occurs simultaneously and exothermally in converting to a metallic silver state.
The conversion of silver oxide to metallic silver as a switching device in a photoflash unit is also well-known for use in the same manner with high voltage type flashlamps. For example, in a more recently issued U.S. Pat. No. 3,990,833, assigned to the assignee of the present invention, there is disclosed a switch material composition having silver oxide mixed with carbon containing silver salt and a humidity resistant organic polymer binder which is converted by the radiant energy provided when a joining flashlamp is fired to metallic silver having a relatively low electrical resistance. The use of silver oxide as the sole silver source in the switching material composition is objectionable as being overly sensitive and proves to react too vigorously during conversion. That is, the silver oxide converts too vigorously and damages the circuitboard or the electrical circuit. Since the continuity of the electrical circuit to the next unfired flashlamp is also likely to be destroyed by such action, a carbon containing silver salt is mixed in the switch material composition to reduce this overall problem. In so doing, the electrical resistance of the converted switch is said to be in the range 0.1-10 ohms.
A need still remains for these switches to exhibit higher electrical conductivity when converted and which is not subject to a violent reaction in photoflash units employing low voltage type flashlamps. Any modification of the switch material composition to accomplish these results must further remain stable under conditions of elevated temperature and high humidity by reason of experiencing such conditions during storage and use.